This invention relates to calcining of carbonaceous material such as petroleum coke, and more particularly to production of a hydrogen-rich product gas stream in a vertical shaft kiln.
Calcination of carbonaceous material such as petroleum coke is carried out routinely. It is known that by maintaining a calcining temperature above about 1400.degree. C. much of the sulfur in the material being calcined can be removed. Such calcination is usually carried out in large inclined rotary kilns. A process for calcining petroleum coke in a moving bed vertical shaft kiln is described in U.S. application Ser. No. 30,251, now U.S. Pat. No. 4,251,323 filed Apr. 16, 1979 by John H. Smith and assigned to the assignee of this application.
It is also well known that hot carbon (above about 315.degree. C.) and steam react according to the water gas reaction C+H.sub.2 O.revreaction.H.sub.2 +CO. This reaction is the basis of much of the effort to gasify coal or other carbonaceous material. A typical gasification process is described in U.S. Pat. No. 3,920,417. That patent describes a process wherein coal is fed to a moving bed retort, oxidizing gas is injected to burn a portion of the coal and heat the remainder, and steam is injected below the ignition level to produce the desired reaction. Product gas is removed from the bottom of the retort.
U.S. Pat. No. 4,007,092 describes a fluid coking and gasification process in which an oxygen-containing gas is introduced into the upper portion of the gasification zone and steam is introduced into the lower portion of the gasification zone.
Both of the processes described in the aforementioned patents are subject to a common deficiency. If air is used as the oxidizing gas, the product gas is heavily diluted with nitrogen. Nitrogen is difficult to remove from the product stream, and if not removed, drastically reduces the heating value per unit volume of the product gas. If the nitrogen dilution problem is avoided by using pure oxygen as the oxidizing gas, then an expensive air separation facility must be provided.
A process of calcining coke and producing synthesis gas is described in U.S. Pat. No. 3,676,517. Again, the process described results in the synthesis gas being diluted with nitrogen when air is used to oxidize coke in the calciner.
There has been a continuing need for a process that could produce a high heating value gas from a gasification process which could utilize air as the oxidizing medium. Such a process is provided by the present invention.